Charles B. Henry, Jr. Institute for Environmental Studies ... fringing Salicornia virginica marsh in Fidalgo Bay, Washington (north- ern Puget Sound) in February ...
SALT MARSH RECOVERY FROM A CRUDE OIL SPILL: VEGETATION, OIL WEATHERING, AND RESPONSE Rebecca Z. Hoff and Gary Shigenaka National Oceanic and Atmospheric Administration Hazardous Materials Response and Assessment Division 7600 Sand Point Way, NE Seattle, Washington 98125 Charles B. Henry, Jr. Institute for Environmental Studies Atkinson Hall, Room 42 Louisiana State University Baton Rouge, Louisiana 70803 beds and the herring spawn that was occurring at the time of the spill, oil was contained along the southern shoreline of the bay using booms. This containment, concurrent with a high tide cycle and northerly winds, resulted in heavy oiling of the fringing salt marsh along the southern edge of the bay. This fringing marsh, dominated by Salicornia virginica and Distichlis spicata, is not pristine (it is adjacent to roadbed fill of a state highway). Nonetheless, the marsh provides increasingly scarce wetland habitat for aquatic organisms and shorebirds. During the cleanup, efforts were made to control access and detrimental impact to the marsh by cleanup workers. Several low-impact cleanup techniques were used in an attempt to remove oil without causing further damage to the marsh. A simple monitoring program was established to document the effectiveness of these response techniques and the recovery of marsh vegetation.
ABSTRACT: Responding to oil spills in marshes is always problematic, since inappropriate response activities can easily add to the overall damage to the marsh. When a spill of Prudhoe Bay crude oil covered a fringing Salicornia virginica marsh in Fidalgo Bay, Washington (northern Puget Sound) in February 1991, response personnel used several low-impact techniques to remove oil from the marsh, and minimized access by cleanup workers. Following the response, we established a monitoring program to track marsh recovery, and to document the effectiveness of the response techniques used and their impacts on the marsh. Through monthly sampling over a 16-month period, we monitored vegetative growth and tracked the chemical degradation of remaining oil. Sampling was conducted along transects located in four areas affected in different ways by the spill, including an oiled, trampled section; an oiled, vacuumed section; and an oiled, washed, and vacuumed section. In addition, a control transect was established in an unoiled adjacent marsh. The study included both biological and chemical components. Biological measurements included percent cover of live vegetation (sampled monthly) and below-ground plant biomass (sampled at the beginning of each growing season in April 1991 and April 1992). Sediment samples included surface sediment (monthly) and core samples collected at the beginning and end of the growing seasons. Sediment samples were analyzed using gas chromatographylmass spectroscopy, and indicator compounds were tracked to determine rates of oil degradation. Results from 16 months of post-spill monitoring show that foot trampling was most detrimental to marsh plants, while washing with vacuuming removed the most oil and minimized adverse impacts to vegetation. Dense clay substrate helped prevent oil from penetrating the sediment, thus minimizing acute toxic effects from oil exposure to marsh plant rootstock. By the second growing season post-spill, Salicornia and other marsh plants were growing in all areas except one heavily oiled patch. The monitoring program will be continued to determine if any delayed impacts occur in the marsh.
Study design and methods In April 1991, four transects were established in the fringing salt marsh along the south end of Fidalgo Bay for the purpose of monitoring vegetative recovery in oiled areas (Figure 1). These transects represented areas affected in different ways by the spill. Transect 1 was a control, located in an unoiled area; transect 2 was located in an area that was relatively lightly oiled but subjected to trampling from extensive foot traffic; transects 3 and 4, both heavily oiled and protected from trampling by the placement of boards over the surface of the marsh, were cleaned in two different ways. Transect 3 was vacuumed with a high-powered industrial vacuum to remove surface oil, while transect 4 was flushed with low-pressure, ambient temperature seawater, and vacuumed similarly to transect 3. Tidal elevations for each transect were measured using standard survey methods, and all sample quadrats were found to be within 0.15 meters of each other (elevations ranged from 2.60 m to 2.76 m). Because of its relatively high elevation, the marsh is flooded infrequently, during exceptionally high tide cycles only. The narrow width of the marsh limited the area available for sampling. In addition, we selected monitoring sites where we were certain that particular treatments had taken place. As a result of these limitations, the study design does not include replicate samples, nor were sample transects or quadrats selected randomly. Our results are there-
In late February 1991, a pump failed during offloading at a Texaco Refinery near Anacortes, Washington, resulting in a spill of North Slope crude oil. Approximately 30,000 gallons of oil entered adjacent Fidalgo Bay, a shallow bay characterized by broad mud flats and large subtidal eelgrass beds. In an effort to keep oil away from the eelgrass
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